1. Field of the Invention
The present invention relates to a magnetic disk drive unit. More particularly, this invention is concerned with an art of determining a position of a data region on a data surface in a magnetic disk drive unit using a data surface servo system.
2. Description of the Related Art
In a conventionally known magnetic disk drive unit using a data surface servo system, tracks (tracks with the same distance from the axis about which a disk rotates is regarded as a cylinder) are formed circumferentially on a data surface of a magnetic disk. Each track is composed of a plurality of sectors (servo sectors). Each sector is composed of a region in which servo information is recorded and a data region succeeding the region in which servo information is recorded and containing data identification (ID). Servo information includes a servo address for use in positioning a head and a burst signal. The servo address is composed of data representing a track number in which a sector concerned exists and data representing the sector number. The data ID includes address information indicating a position of a data region (that is, data indicating a track number and a sector number which specify a sector concerned). In other words, the servo address and the data ID have mutually similar address information.
In execution of read/write processings for a data region on a data surface having the foregoing data structure, a data ID preceding the data region must be interpreted in order to determine the position of the data region.
In recent years, constant density recording has been adopted in an effort to increase storage capacity. In constant density recording, the number of data sectors (comparable to data regions) per track is changed between an outer circumference of a magnetic disk and an inner circumference thereof in order to ensure constant recording density for the whole of the magnetic disk. This poses a drawback in that a data sector may stay over two adjoining servo sectors on the same track; that is, what is referred to as "data split" may occur.
In a conventional magnetic disk drive unit, reading or writing is controlled by appending split information to the aforesaid data ID. The data ID contains not only address information indicating a position of a data region and split information but also defect information indicating presence or absence of a defect in the data region. The defect information is used to replace a defective data region by an indefectible data region.
As mentioned above, as long as a conventional magnetic disk drive unit using a data surface servo system is concerned, servo address for use in positioning a head on a desired track and data ID for use in identifying a data region have mutually identical address information. In other words, the same address information (data indicating a track number and a sector number) is duplicated.
If one of duplicated address information contained in servo information can be omitted, a region from which the address information is omitted can be used to record extra data. This is preferable from the viewpoint of storage capacity.